"They left the tanks bone dry and when the drivers tried to start them, two of them conked out straight away," Mr Jolley said.

"There's £2,000 worth of fuel gone and we had to call out the local Scania agent and there's about £250 gone there and we've had seven vehicles that were running behind schedule - that's quite a big cost to the company.

"They've come in from an adjacent property and used quite a heavy duty machine because they stole about 2,000 litres out of the HGVs. What they've done is pumped it over a 6ft fence and up a 15ft embankment.

"It was definitely organised and they knew what they were doing. They were doing it from nearby flats, and you can still see the diesel residue, where they've done it. They were quite selective in the ones they picked."

Rising fuel prices are believed to be behind a spate of thefts involving haulage firms, and last week a tanker was also targeted by petrol pirates on the A12 near Lowestoft, though the gang left empty-handed.

John Howells, regional director of the Road Haulage Assocation, said the raiders were often highly organised.

Insp Russell Watkins, from the Earlham, Lakenham and Marlpit Safer Neighbourhood Team (SNT) said hauliers and people storing large amounts of fuel should remain vigilant and take the necessary steps to protect their fuel.

"A rise in the price of fuel,

which we have seen recently,

can make it an attractive target

for opportunist thieves," Insp Watkins said. "Therefore

Norwich residents and businesses must be on their guard."

Mr Jolley said it was not the first time the firm's lorries had been targeted and he had also warned other haulage companies about the theft.

"We've fallen prey to having vehicles locked up in the country by the roadside having their fuel stolen," he added. "This time the vehicles were in our locked compound, which is lit and got security cameras

Thieves struck between 2.50pm on Saturday and 5.15am on Monday. The fuel caps on the vehicles were not damaged, with

a trail of diesel being the only

sign of a break-in.

Officers would like to hear from anyone who may have noticed anything suspicious in the area between the times stated or from anyone with information in relation to the suspects.